1. Field of the Invention
The present invention relates to a planar type display device for use in a color television receiver or a terminal display of a computer and its driving method.
2. Description of the Prior Art
In an electrode structure in a conventional planar type display device, generally a group of laminated electrodes is constructed by bonding, pressure bonding or merely laminating them together. A proposal of a method of bonding the laminated electrodes has been already made by the same applicant in the Japanese patent laid open 102138/1988. This conventional electrode structure is shown in FIG. 1. The structure and the operation of this conventional proposal is briefly explained below.
In this electrode structure, there are provided a back electrode 101 with a plurality of shelves, filament cathodes 102 located between the shelves for generating electron beams, a vertical focussing electrode 103 for vertically focussing the electron beams, vertical deflection electrodes 104 for vertically deflecting the electron beams, electron beam control electrodes 105 for controlling the amount of the electron beams passing therethrough, a horizontal focussing electrode 106 for horizontally focussing the electron beams, horizontal deflection electrodes 107 for horizontally deflecting the electron beams, electron beam accelerating electrodes 108 and a screen 109 on which the electron beams impinge to display a picture in turn from the rear side to the front side. These components are accommodated in a container made of glass in the order of the above arrangement and the inside of the container is vacuumized. The electron beam generated by the filament cathode 102 is pushed forward by the back electrode 101. A signal modulation voltage which is obtained by converting an image signal into a pulse width modulation signal is applied to the respective electron beam control electrodes 105, whereby the amount of the electron beams passing therethrough is controlled. The screen 109 is coated with fluorescent members for emitting the light of three colors R (red), G (green) and B (blue). In this conventional example, the laminated electrode group consists of the vertical focussing electrode 103, vertical deflection electrodes 104, electron beam control electrodes 105, horizontal focussing electrode 106 and horizontal deflection electrodes 107. Also the vertical focussing electrode 103 and the horizontal focussing electrode 106 may be composed of a plurality of laminated electrode members.
The operation of this conventional example is explained below. A pulse voltage having a negative value is applied to one of the filament cathodes 102 so that an electron beam band is generated in the forward direction. The electron beam band is focussed in the vertical direction through the vertical focussing electrode 103. Thereafter, the vertically focussed electron beam is deflected in the vertical direction in 32 steps for example including an interlaced scan through the vertical deflection electrode 104. The amount of the electron beam to pas is controlled by the electron beam control electrode 105 in accordance with the image signal applied thereto. Thereafter, the electron beam is passed to the horizontal deflection electrode 107 through the horizontal focussing electrode 106, whereby the electron beam is horizontally deflected in six steps in a period of one horizontal scan. Each of the divided electron beams impinges on two pairs of fluorescent units for the three colors in turn of R - G - B to R - G - B, thereby emitting light for the three colors to display a picture band on the screen 109. This operation is sequentially repeated to display a series of picture bands thereby to display a complete picture.
This conventional device is intended to solve such a problem that, in a process of sintering for bonding the respective electrodes, when the electrodes are heated up to 450.degree. C. which is the melting temperature of low melting frit glass, there occurs a temperature difference in the respective electrodes of the laminated electrode group, and therefore the electrodes can not be securely bonded with a high accuracy. The aim of this proposal is attained by keeping the temperature of the electrodes in a range of 330.degree. C. to 370.degree. C. for more than ten minutes, whereby the temperature difference can be decreased thereby to securely bond the electrodes with a high accuracy. The securely bonding condition of the laminated electrodes in the sintering process is shown in FIG. 2.
In this proposal, there was such a further problem that, since an interior of a panel is made vacuum in the intermediate step of subjecting to the thermal process, the atmospheric pressure is applied to the laminated electrodes, so that the electrodes are brought into their pressure bonding conditions with different thermal expansions respectively because the electrodes have different thermal expansion factors. Therefore, when the temperature of the electrodes is lowered to the room temperature, the friction forces generated in the electrodes are so large that each electrode can not recover the original formal location.
In order to solve this problem, a further proposal has been made by the same applicant in the Japanese patent laid open 124936/1989. This second proposal discloses a process of securely forming the laminated electrodes by pressure bonding. That is, after performing the thermal process, the circumference of the exterior of the panel is temporarily made vacuum, so that the pressure bonding condition of the laminated electrodes in the panel is temporarily released from the atmospheric pressure, thereby to recover the original locating condition of the electrodes with a high accuracy.
Moreover, a further proposal is made by the same applicant in the Japanese patent application 103801/1989, wherein the electrodes are slidably held when the electrodes are thermally expanded in the heating process. In this third conventional structure, the electrode plate has a warped portion therein and it is difficult that the whole plate becomes slidable, and that there often occur strong pressure bonding portions at the warped portions so as to expand the warped portions.
The three conventional examples of the prior art mentioned above are proposed for suppressing the decrement of the accuracy of locating the electrodes due to the different expansion factors thereof in the heating process of the laminated electrodes for securely forming a group of the laminated electrodes. Conventionally, it has been thought that the deterioration of the electrode accuracy is caused in the heating process for securely forming the electrodes. However, recently it has become apparent that the deterioration of the accuracy is caused not only by the heat in the above heating process but also by the effect of the heat generated by the filament cathodes arranged in the panel. Namely, it has become apparent that the major causes, which deteriorate the accuracy of locating the electrode so as to deteriorates the picture quality, are both the heat generated in the electrode forming process and the heat generated by the cathodes themselves while the panel is lighted on.
Moreover, it has become apparent that there is a further problem as mentioned below. After the panel is completed, when a number of filament cathodes are actually turned on, the temperature of the respective electrodes near to the filament cathodes rises considerably. On the other hand, the temperature of the electrodes in the distance away from the filament cathodes becomes lower. Therefore, there occurs thermal expansion differences among the electrodes, whereby the electrodes are partially expanded and contracted in a similar manner to those in the prior art as mentioned above. Consequently, there occur errors in the pitches and the like of holes of the electrodes through which electron beams pass, wherein the pitches of the electrodes are initially set in correspondence with the positioning of the respective parts of the fluorescent face, so that the electron beams can not be landed to the predetermined points on the fluorescent face, resulting in deterioration of the picture quality. On the other hand, while the panel is driven, the electron beams impinge on the light emitting means which is formed by coating the fluorescent member on a glass plate, and the temperature of the glass plate rises. At this time, since the thermal expansion of the laminated electrode group is different from that of the glass plate of the light emitting means, there occurs a further problem that the electron beams become unable to impinge on the predetermined points of the fluorescent face with time, although it does not become a problem for a small size panel but becomes a problem for a large size one.